The present invention relates to an injection mold comprising
an injector mold plate having a first injector mold plate face including first mold cavities halves of one or more mold cavities and an opposite second injector mold plate face to be mounted to an injection molding tool,
an ejector mold plate having a first ejector mold plate face including second mold cavities halves of one or more mold cavities and an opposite second ejector mold plate face to be mounted to an injection molding tool,
the first injector mold plate face faces towards the first ejector mold plate face to delimit one or more mold cavities when the injector mold plate and the ejector mold plate are in closed contact during injection of a plastic material, and
at least one tempering medium channel that connects at least a tempering medium inlet of the injection mold to a tempering medium outlet of the injection mold.
International patent application no. WO2013/126723 includes a discussion of conventional cooling systems for injection molding machines. The cooling system accelerates cooling of the molded parts by circulating a cooling fluid through the mold, thereby allowing the machine to complete more cycles in a given amount of time, which increases production rates and thus the total amount of molded parts produced. It is emphasized that these cooling systems add complexity and costs to the injection molds, a.o. because of costly designing of complex hole patterns, drilling long holes in 3D, manually plugging holes, many setups in different directions, and because high hardness mold materials are difficult to machine. Leakage of cooling fluid must not take place during the injection molding cycle. So in order that cooling fluid does not leak to the exterior of the mold cooling channels are conventionally made by drilling holes in the support plates, thus cooling channels are straight and embedded, and only a limited number of criss-crossing cooling channels, optionally in several planes, are possible within the thickness of a base plate or support plate for an injection mold. Moreover, it is impossible to approximate the distance so that said distance is substantially uniform to all mold cavities of an injection mold.
Accordingly, drilling of cooling channels through the base plate or support plate is difficult, time consuming, and expensive. Moreover, cooling channels can only be drilled in a straight line, resulting in that critical hotspots often remain out of reach of the cooling/heating medium and therefore cannot be mitigated. These practical limitations in drilling cooling channels result in unequal cooling within the injection mold which has consequences on the quality of the molded part.
WO 2003/011550 discloses various mold assemblies having a plurality of cooling lines machined in a support plate to facilitate injection molding thin-walled parts without the thinness of the flow channel cools the molten thermoplastic material before this material reaches the end of the flow channel and fills the cavity completely. This known injection mold has an integrated shell that is constructed of both a surface layer of the mold cavity with low thermal mass and an insulation layer which is located on the surface of the reverse side of the surface layer and comprises micro-channels or micro-holes. Heating of the cavity surfaces during injection of thermoplastic material takes place by induction heating, and subsequent cooling of the molded part is obtained by circulating a cooling fluid through a cooling line installed in the mold base or through the micro-channels constructed in the insulation layer. To minimize risk of leakage of cooling fluid the microholes and micro-channels are internal bores, as in any other conventional injection mold, and only a limited amount of cooling fluid can be circulated. It is proposed without any technical teaching and indication of means that heating also can take place through the drilled bores by circulating a fluid at high temperature through a cooling line or the micro-channels.
In summary, in the above conventional injection molding systems using cooling channels, such cooling channels are integral bores through which a minimum of cooling fluid can pass at a limited speed to reduce potential leakage. Thus, in such cases, although the conventional cooling methods enable fast production compared to conventional injection molding methods not applying active cooling, the cooling process still needs to be made more effective, e.g. to injection molding complex parts, including thin parts, as well as for improving production rates, minimize costs and deliver high quality.
WO9731733 relates to a casting process to make cavity and core inserts for injection molding tools. These inserts are cast with a fluid circulator system that moves or pulls a cooling fluid into a cooling chamber on the backside of the inserts. The cooling fluid is subjected to a negative pressure to rapidly pull the cooling fluid through the chamber. The cooling fluid is agitated around support pillars provided in the chamber to provide strength to the inserts.
An alternative embodiment of a cooling chamber of WO9731733 has support means comprising a plurality of congruent wall sections, which axially extend from the front side of an insert. The support wall sections are symmetrically positioned in the chamber so when the plastic material is injected into the cavity area there is more support where the plastic material is under the high injection pressure. During operation of the molding apparatus outside pressure bearing means act to absorb or bear the brunt of the high pressure exerted against the core insert and the cavity insert. The pressure bearing means have a height slightly longer or taller than the combined depth of the core insert and the cavity insert such that most of the molding pressure is absorbed by said pressure bearing means so as to reduce stress or pressure put on the inserts to force the melt to distribute inside the one or more mold cavities. So WO9731733 produces injection molds for high pressure applications without heating the mold. Further these injection molds are cast on a model of the plastic part in a two-step process where the molding cavities are formed during casting. Such molded cavities are however rarely molded to correct size since the cast metal material shrinks substantially during hardening. In particular the copper proposed in WO9731733 has high shrinkage compared to aluminum and gray steel.
The support wall sections define a flow chamber of channels all of which in mutual fluid-connection via traverse openings. As a cooling fluid is pulled through the open chamber, the flow of the fluid is disturbed as it passes around the support pillars and/or wall sections and allows water to flow wherever it finds the shortest way, thus the flow path of the water cannot be controlled. The flow path is arbitrary if negative pressure is applied, so the flowpath is as directly as possible from a cooling fluid inlet to a cooling fluid outlet.
WO9731733 does not propose to use the cooling chamber for heating the mold cavities as well, and thus have no need for any kind of insulation to administer thermal energy.
There is thus still a need within the art of injection molding to get cheaper and simpler manufacturing of the tempering arrangements for the injection mold, and to optimize heat exchange between plastic material and injection mold during a molding cycle to obtain short cycle time, thus increased productivity, as well as molding plastic products of high quality.